PREDICTING RANGE OF MOVEMENT AFTER KNEE REPLACEMENT: THE IMPORTANCE OF POSTERIOR CONDYLAR OFFSET AND TIBIAL SLOPE

Abstract

Background: The determinants of range of movement following knee replacement may be surgically modifiable (tibial slope, posterior condylar offset or the level of the joint line) or non modifiable (pre-operative range of movement, sex or BMI). We aimed to quantify the influence of these factors upon restoration of flexion in the arthritic knee following knee replacement

Methods: Patients were included from two prospective trials for three different designs of knee replacement. Range of movement was recorded using a standard measuring technique preoperatively and 12 months after surgery. Radiological measurement was done by an independent observer and included the preoperative posterior condylar offset and the postoperative tibial slope, posterior condylar offset, posterior condylar offset ratio, varus-valgus alignment and Insall ratio. Multivariate analysis using stepwise selection was performed to determine the significant predictors of the range of movement at 12 months.

Results: The study includes 133 knee replacements performed on 125 patients. Complete clinical and radiographic data for preoperative and 12-month assessment was available for 101 knees and only these were included for the analyses. There was no significant difference between the three groups in terms of postoperative range of movement or the radiological parameters measured. Multivariate analysis after adjusting for age, sex, diagnosis and the type of prosthesis revealed that the only significant correlates of range of movement at 12-months were the difference in posterior condylar offset ratio, tibial slope and preoperative range of movement. Moderate correlation was noted between range of movement at 12 months and posterior tibial slope (R=0.58) and the difference of post femoral condylar offset (that is, post-operative minus preoperative posterior condylar offset, R=0.65). Preoperative range of movement had only a weak correlation with post-operative range of movement (R=0.20).

Conclusions: We found that the posterior femoral condylar offset had the greatest impact upon final range of movement. We would encourage the operating surgeon at pre-operative templating to take this into account when choosing size and design of femoral component.